Often a sample of blood or joint fluid can help you doctor confirm a diagnosis. For example, a blood test showing high blood levels of rheumatoid factor – an antibody that acts against the blood component gamma globulin – or an antibody called anti-cyclic citrullinated peptide antibody (anti-CCP) may suggest rheumatoid arthritis. High levels of antinuclear antibodies (ANAs), abnormal antibodies directed against the cells' nuclei, could suggest lupus or another inflammatory disease. A high erythrocyte sediment rate (ESR, or sed rate), along with muscle pain in the shoulders, could help confirm a diagnosis of polymyositis or polymyalgia rheumatica.

Tests of fluid drawn with a needle from the joint may reveal crystals of uric acid, confirming a diagnosis of gout; calcium pyrophosphate dehydrate, confirming pseudogout; or a bacterium, suggesting that joint inflammation is caused by an infection. 

If your doctor suspects your pain may be caused by disease of the heart, liver, gallbladder or other organ or area of the body, different types of blood tests may aid in the diagnosis of those problems.

Learn more about lab tests used in diagnosing arthritis.